1. Field of the Invention
This invention pertains to the field of hand tools. More particularly, this invention pertains to a device to hold rotating propellers such as those on boats or other watercraft to allow them to be safely removed.
2. Background of the Invention
Watercraft are an almost ubiquitous part of human society. Wherever there are open expanses of water, humans can generally be seen afloat on the surface in some form of marine vehicle. While many marine vehicles are powered by wind or direct human effort through paddling or rowing, many more watercraft are powered by motors. These motorized watercraft come in a wide variety of sizes and designs from small personal watercraft designed to carry one person to the gigantic aircraft carriers of the United States Navy.
Particularly with regards to private watercraft, regardless of the design, these watercraft are usually propelled by similar mechanisms. In particular, these watercraft utilize outboard or inboard/outboard motors which are attached to the transom. The motor is attached to a steering column (or has a simple handle attached thereto) to allow the motor to be rotated relative to the body of the watercraft.
In normal construction and when in standard operation, the motor generally comprises an engine portion which is at the top of the motor and is attached so as to ride above the water in normal operation. This engine is then connected to a generally vertical drive shaft which extends downward (generally within a housing) and passes through the surface of the water. At the bottom of the vertical drive shaft there is a connection to a horizontal drive shaft which extends generally parallel to a direction of movement. Attached about the rotational axis of the horizontal drive shaft is a propeller which comprises a generally cylindrical hub placed around the drive shaft with two or more blades projecting from the outer surface thereof at an angle to the hub. When in use, the engine drives the drive shafts causing them both to rotate about their axes. The hub then rotates about its major axis in conjunction with the horizontal drive shaft in turn rotating the blades through the water. Because of the positioning of the blades at an angle to the axis of rotation, the blades displace the water pushing the back end of the boat in a direction generally parallel to the horizontal drive shaft (or hub) of the motor.
Translation of the rotational energy from the horizontal drive shaft to the hub and therefore the blades is usually accomplished through the use of a shearable pin or friction device to allow translation of the rotational energy of the drive shaft into rotation of the propeller. Typically, the propeller will be attached to the drive shaft through the use of a retaining nut placed on the end of the drive shaft that holds the propeller on the drive shaft when in operation.
In order to remove the propeller, the nut is removed and the propeller hub can be pulled off of the drive shaft. The problem with this operation is that the drive shaft and propeller are designed to rotate together and the internal gearing generally cannot be used to lock the drive shaft (and propeller) in place when the nut is turned (whether to loosen or to tighten it). Therefore, when a user tries to rotate the nut he simply rotates the drive shaft and propeller and does not turn the nut as the rotation of the drive shaft is usually easier than the rotation of the nut relative to the drive shaft.
Because the drive shaft is generally located within the propeller hub, it is often impractical to directly prevent the drive shaft from rotating. Instead, when a user (such as a boat owner or repairman) wants to turn the nut, he will generally attempt to constrain the motion of the propeller relative to the nut, which is turn constrains the motion of the drive shaft and allows the nut to rotate relative to the drive shaft. In this way, when torque is applied to the nut, the nut can turn while the drive shaft is constrained allowing the nut to be tightened or loosened on the drive shaft.
There were a few different procedures which have been used to constrain the propeller from rotating. In the simplest one, the user grasps at least one of the blades of the propeller with his hand and he then pushes against the propeller at the same time he attempts to rotate the nut with a wrench. The combination of equal torque on both the blade in one direction and the nut in the other direction prevents the propeller and drive shaft from rotating. However, as only one direction of torque is on the nut, the nut can rotate relative the drive shaft.
The problem with this procedure is that it is quite dangerous. The blades of a propeller can be quite sharp so as to facilitate the motion of the watercraft through the water. Further, the nut will often be slightly corroded and/or may be designed to lock in place meaning that turning the nut may be very difficult at the start, but once a seal is broken it may turn very easily. It is therefore often the case that the user will grasp a blade and place a significant amount of force against the propeller and nut attempting to break the seal of the nut. When the nut suddenly begins to turn, the forces are suddenly no longer resisted and the user's hand can slip against the blade injuring him. The user's hand on the blade also may not be able to generate as much force as the user's hand on the wrench can generate (as the wrench handle serves as a lever arm allowing mechanical advantage). This can result in the user's hand being pulled into the housing of the vertical drive shaft or the anti-cavitation of the motor plate also causing injury.
To try to get around this problem of potential injury to the user's hand, the user can place a brace of some form in the propeller and the housing instead of holding the blade with their hand. This brace essentially serves as a barrier to the propeller blade to not rotate past a certain point relative the housing. In its simplest embodiment, a user may just put a board or similar object between two of the propeller blades and against the housing. As he then turns the nut, the blades wedge the board between themselves and the housing preventing movement of the propeller in the direction the user is attempting to turn the wrench and the torque applied by the user keeps the brace from moving. In more complicated embodiments, the same concept has also been used to develop devices which can be rigidly attached to the motor housing. U.S. Pat. No. 4,850,800 provides an embodiment of one such bracing device.
The problem with all these methods and devices is that they place a lot of force on the edge of the blade at the tip of the blade (where the blade is thinnest) and the blade can easily be damaged by the device being used to block the movement. Further, because of the direction of rotation of the blade, the forward edge of the blade is sometimes against the barrier. As the forward edge is often thinner than the trailing edge, the design of the forward edge is generally more sensitive to damage from this contact.
Further, braces such as these are generally held in place by mechanical means and may come loose or break as the user does not know how much force can be applied before the device will suddenly release. In these systems, the connection of the brace to the motor housing is the potential weak point of connection and this connection can slip if the user applies too much force to the nut. This can result in a sudden movement of the propeller and possibly the brace being thrown. Both of these situations can also be dangerous to the user.
Some devices have been developed for grasping the rotating blade of a lawnmower to hold that blade steady while the user removes the nut holding the blade to the lawnmower. One such device is shown in U.S. Pat. No. 4,564,991. Devices for holding lawnmower blades, however, are generally not suitable for holding propeller blades. When grasping the lawnmower blade, the devices grasp from the leading to the trailing edge of the blade (they grasp the side of the blade). For a lawnmower, the blade is very strong so this is acceptable. On a boat propeller blade, this type of grasping is likely to bend the blade which can result in severe damage to the blade rendering it unusable. Further, as a propeller blade is generally bent relative to the hub so as to provide for motive force in the water, the leading and trailing edges of the blade are spaced from each other in the direction of rotation of the propeller and they are also spaced from each other in the direction of the axis of the propeller. Therefore, grasping the leading and trailing edges simultaneously will generally result in the tool not being a lever arm in the plane of rotation, but being arranged at an angle to the rotation which makes the transfer of force less efficient.